Basically, I am building a robot that needs to be able to detect the distance from multiple sides. My plan is to use multiple ultrasonic range finders on each side, but I'm worried about interference between the sensors. Do there exist sensors that output and receive different frequencies to ensure that they don't interfere with each other?
Electronic – Two different ultrasonic range finders to minimize interference
proximity-sensorsensor
Related Solutions
A typical piezoelectric ultrasonic transducer won't be as efficient when driven at frequencies other than it's rated one. They act a bit like a resonant LC tank, so sensitivity drops off quite sharply.
A typical figure seems to be ~2kHz -6dB bandwidth (e.g. with 40kHz transducer if will be half as sensitive or give half the output at 39kHz and 41kHz)
40kHz seems to be the most common (and cheap) but you can get different frequencies like 25kHz, 60kHz, 180Khz, etc.
Rather than doing this though, why not just use 4 of the same and pulse each one separately, or use one and rotate through desired angle with servo.
Unless your robot is travelling very quickly it shouldn't matter if you stagger the pulses slightly.
You can even make a basic SONAR this way, here's an interesting PIC based example.
Depending on what the shape of the treadmill is (could you provide a picture?) you could use the LEDs by making diagonal lines between the side bars and the floor of the treadmill.
Something like this:
where red circles are IR LEDs and green circles are receivers or vice versa, with some logic work should give you the control over the position of the dog.
You will have some interference between the LEDs but you can use modulation or some form of synchronization to deal with it.
Best Answer
The usual approach is to trigger only one sensor at a time. In other words, time-division multiplexing, rather than frequency-division multiplexing.
Otherwise, even if the sensors aren't pointing in the same general direction, coupling through the structure of the robot itself can create unnecessary interference.
Just to put some numbers with that: Ultrasound requires about 6 ms per meter of sensed distance. If you're interested in distances up to 2 meters from your robot, then each sensor needs 12 ms. If you have 8 sensors, that's a total of about 100 ms, which means that each one can take 10 measurements a second. This should be plenty for a robot that can move at up to several meters/second, depending on how quickly it can stop, of course.